Neurotrophins, neuromitogens, and other growth factors are soluble proteins necessary for the survival and/or function of specific neuronal populations throughout the life of an organism. Because of their significance to the nervous system, these factors nave been extensively studied to gain a basic scientific understanding of their signaling mechanisms and the role they play during neural development. In addition, since growth factors have been shown to promote the survival of a wide variety of neuronal subtypes, interest in applying them to treat a variety of neurodegenerative disorders and trauma has soared in recent years. Fundamental, mechanistic studies of growth factor signaling and cellular response may yield information of interest for understanding of their role during development, in the adult, and in aged animals. This proposal addresses the hypothesis that the quantitative nature of growth factor signaling is important in determining target cell response. To address this hypothesis, the specific goals are: i) To characterize the proliferative and/or differentiative responses of neural precursors to different growth factors, ii) To quantify the growth factor-stimulated signal in the primary neural precursors and analyze whether the quantitative nature of the signal correlates with cell fate, iii) To determine whether cell fate can be influenced by levels of a growth factor receptor.